Resistance and the control of lice on humans and production animals

Phthiraptera (lice) are specialised insects adapted to parasitise many warm-blooded vertebrates, including domestic animals and humans. Often, attempts by the host to alleviate the irritation created by lice, causes derangement of the hair/fur coat. Unless treated, this derangement may cause economic losses due to hide damage and/or downgrading of wool/hair/fur. In 1981, application of aqueous insecticide solutions (dipping) for the control of sheep body lice (Bovicola ovis) was largely superseded by off-shears pyrethroid "pour-on" treatments. By 1985, several field failures with these products were found to be due to low-level (20x) insecticide resistance. In 1990, high-level (640x) resistance was diagnosed in a New South Wales population. However, despite 30+years use, organophosphate-based products are still usually effective. Until recently, cattle lice caused little concern. Treatments were applied mainly for aesthetic reasons when cattle were to be presented for sale, and also to prevent damage to fences by rubbing cattle. However, the introduction of quality-management programmes have raised awareness of the economic losses due to hide damage associated with lice infestations. Emerging industries such as emu and alpaca farming have raised the pest status of other louse species, and necessitated insecticidal intervention. In humans, attempts to control head lice, Pediculus humanus capitis, infestations have repeatedly failed around the world.     

Head lice in Norwegian households: actions taken, costs and knowledge

Introduction

Head lice infestations cause distress in many families. A well-founded strategy to reduce head lice prevalence must shorten the infectious period of individual hosts. To develop such a strategy, information about the actions taken (inspection, treatment and informing others about own infestations), level of knowledge and costs is needed. The present study is the first to consider all these elements combined.

Materials and Methods

A questionnaire was answered by 6203 households from five geographically separated municipalities in Norway.

Results

94% of the households treated members with pediculicides when head lice were discovered. Nearly half of the households checked biannually or not at all. Previous occurrence of head lice and multiple children in a household improved both checking frequency and method. More than 90% of the households informed close contacts about their own pediculosis. Direct costs of pediculosis were low (less than €6.25 yearly) for 70% of the households, but the ability to pay for pediculicides decreased with the number of head lice infestations experienced. One in three households kept children from school because of pediculosis. Other widespread misconceptions, such as that excessive cleaning is necessary to fight head lice, may also add unnecessary burden to households. School affiliation had a significant effect on checking frequency and method, knowledge and willingness to inform others about own pediculosis.

Conclusions

Increased checking frequencies appear to be the most important element to reduce head lice prevalence in Norway and should be a primary focus of future strategies. National campaigns directed through schools to individual households, might be an important tool to achieve this goal. In addition to improving actions taken, such campaigns should also provide accurate information to reduce costs and enhance the level of knowledge about head lice in households.     

Consumption of drugs for sea lice infestations in Norwegian fish farms: methods for assessment of treatment patterns and treatment rate

Sea lice are a major problem in Norwegian fish farms; however, data on drug treatment patterns or treatment rates of sea lice infestations are not available. Such data are important for analysing resistance patterns against drugs used for such infestations. The main objective of the present study was to develop a method to estimate the treatment patterns and treatment rates for drugs used in the treatment against sea lice (Lepeophtheirus salmonis and Caligus elongatus) in farm salmonids by means of national sales statistics. Annual sales figures, as weight of active substances, were obtained from the drug wholesalers and the feed mills. The weight of active drug substances is not useful as a unit of measurement of drug use in an epidemiological context because it does not correct for dosage differences and number of repeat treatments. To correct for these factors, we introduced approved daily dose (ADD(farm fish)) and treatment course-doses(farm fish) kg(-1) live-weight fish. To express the drug treatment patterns, the biomass (in weight) of farm salmonids treated with 1 course of a drug were estimated. When measured as kg active substance, the quantities of drugs for the treatment of sea lice infestations declined by 98% during the study period (1989 to 2002) but this figure increased 5-fold when it was corrected for differences in dosage. To correct for amounts of farm salmonids liable to require treatment we estimated the annual treatment rate, defined as the number of treatments for sea lice infestations per biomass slaughtered Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss. The annual treatment rate increased gradually during the study period; however, it varied considerably (range 0.45 to 1.34, mean 0.90). Before 1995, organophosphates were the most frequently used drugs against sea lice; since then pyrethroids have become the dominating drug group.     

Infestation of people with lice in Kathmandu and Pokhara, Nepal

The prevalence of infestation with head lice and body lice, Pediculus spp. (Phthiraptera: Pediculidae) and pubic (crab) lice Pthirus pubis (L.) (Phthiraptera: Pthiridae), was recorded from 484 people in Nepal. The prevalence of head lice varied from 16% in a sample of people aged 10-39 years of age, to 59% in street children. Simultaneous infestations with head and body lice (double infestations) varied from 18% in slum children to 59% in street children.     

Evidence from double infestations for the specific status of human head lice and body lice (Anoplura)

Abstract Samples of head lice and body lice obtained from Ethiopians suffering from double infestations were mounted onto microscope slides and measured. The mean length of body lice (♀ 4.4mm; ♂ 3.8mm) was greater than that of head lice (♀ 3.5 mm; ♂ 2.9mm), but the best discriminant was the length of the tibia of the middle leg (♀ 425/296 μ♂421/291 μ). No intermediate specimens were found in these double infestations, although intermediates can can be produced experimentally by cross-mating. Since populations of head lice and body lice remain distinct it is concluded that they represent two distinct species, Pediculus capitis De Geer and P. humanus Linneaus.     

The head and body lice of humans are genetically distinct (Insecta: Phthiraptera, Pediculidae): evidence from double infestations

Little is known about the population genetics of the louse infestations of humans. We used microsatellite DNA to study 11 double infestations, that is, hosts infested with head lice and body lice simultaneously. We tested for population structure on a host, and for population structure among seven hosts that shared sleeping quarters. We also sought evidence of migration among louse populations. Our results showed that: (i) the head and body lice on these individual hosts were two genetically distinct populations; (ii) each host had their own populations of head and body lice that were genetically distinct to those on other hosts; and (iii) lice had migrated from head to head, and from body to body, but not between heads and bodies. Our results indicate that head and body lice are separate species.     

Spatial and temporal variations in sea lice (Copepoda: Caligidae) infestations of three salmonid species farmed in net pens in southern Chile

Sea lice infestations have become a major health problem for farmed salmonids throughout the world including Chile. In southern Chile, 6 geographical areas, divided into 22 geographical zones with a total of 127 salmon farming centers and 1519 sea pens, were regularly sampled from December 1999 to April 2002. A linear mixed-effects model (LME) approach was used to describe the infestations of adult forms of sea lice on 3 salmonid species farmed in southern Chile. The variables fish species, water temperature, water salinity, fish weight, juvenile parasite count, pen shape, treatment status in previous month and the interaction of previous and current month treatments were found to be statistically significant fixed effects for the population sampled. The most susceptible species to sea lice infestation was rainbow trout Oncorhynchus mykiss, while the least susceptible species was coho salmon O. kisutch. Fishes in pens treated in the previous month with avermectins were associated with the smallest sea lice count compared to fishes in pens not treated or treated with other products. The variability in sea lice infestations in areas and zones within areas was not statistically significant when controlling for the previously mentioned fixed variables. The variability between centers, the within-pen variability, and the interaction between within-pen effect and the date of measurement were statistically significant and not explained by the fixed effects. Potential sources for this variability are discussed. We conclude that the epidemiology of sea lice infestations in farmed salmonids in southern Chile is complex and in need of further study.     

What's in a name: the taxonomic status of human head and body lice

Human head lice (Anoplura: Pediculidae: Pediculus) are pandemic, parasitizing countless school children worldwide due to the evolution of insecticide resistance, and human body (clothing) lice are responsible for the deaths of millions as a result of vectoring several deadly bacterial pathogens. Despite the obvious impact these lice have had on their human hosts, it is unclear whether head and body lice represent two morphological forms of a single species or two distinct species. To assess the taxonomic status of head and body lice, we provide a synthesis of publicly available molecular data in GenBank, and we compare phylogenetic and population genetic methods using the most diverse geographic and molecular sampling presently available. Our analyses find reticulated networks, gene flow, and a lack of reciprocal monophyly, all of which indicate that head and body lice do not represent genetically distinct evolutionary units. Based on these findings, as well as inconsistencies of morphological, behavioral, and ecological variability between head and body lice, we contend that no known species concept would recognize these louse morphotypes as separate species. We recommend recognizing head and body lice as morphotypes of a single species, Pediculus humanus, until compelling new data and analyses (preferably analyses of fast evolving nuclear markers in a coalescent framework) indicate otherwise.     

Why infest the loved ones--inherent human behaviour indicates former mutualism with head lice

Head lice transmit to new hosts when people lean their heads together. Humans frequently touch their heads to express friendship or love, while this behaviour is absent in apes. We hypothesize that this behaviour was adaptive because it enabled people to acquire head lice infestations as early as possible to provoke an immune response effective against both head lice and body lice throughout the subsequent periods of their life. This cross-immunity could provide some defence against the body-louse-borne lethal diseases like epidemic typhus, trench fever, relapsing fever and the classical plague. Thus the human 'touching heads' behaviour probably acts as an inherent and unconscious 'vaccination' against body lice to reduce the threat exposed by the pathogens they may transmit. Recently, the eradication of body-louse-borne diseases rendered the transmission of head lice a maladaptive, though still widespread, behaviour in developed societies.     

Pair of lice lost or parasites regained: the evolutionary history of anthropoid primate lice

Background  

The parasitic sucking lice of primates are known to have undergone at least 25 million years of coevolution with their hosts. For example, chimpanzee lice and human head/body lice last shared a common ancestor roughly six million years ago, a divergence that is contemporaneous with their hosts. In an assemblage where lice are often highly host specific, humans host two different genera of lice, one that is shared with chimpanzees and another that is shared with gorillas. In this study, we reconstruct the evolutionary history of primate lice and infer the historical events that explain the current distribution of these lice on their primate hosts.     

Head Lice Surveillance on a Deregulated OTC-Sales Market: A Study Using Web Query Data

The head louse, Pediculus humanus capitis, is an obligate ectoparasite that causes infestations of humans. Studies have demonstrated a correlation between sales figures for over-the-counter (OTC) treatment products and the number of humans with head lice. The deregulation of the Swedish pharmacy market on July 1, 2009, decreased the possibility to obtain complete sale figures and thereby the possibility to obtain yearly trends of head lice infestations. In the presented study we wanted to investigate whether web queries on head lice can be used as substitute for OTC sales figures. Via Google Insights for Search and Vårdguiden medical web site, the number of queries on “huvudlöss” (head lice) and “hårlöss” (lice in hair) were obtained. The analysis showed that both the Vårdguiden series and the Google series were statistically significant (p<0.001) when added separately, but if the Google series were already included in the model, the Vårdguiden series were not statistically significant (p = 0.5689). In conclusion, web queries can detect if there is an increase or decrease of head lice infested humans in Sweden over a period of years, and be as reliable a proxy as the OTC-sales figures.     

Evidence that clade A and clade B head lice live in sympatry and recombine in Algeria

Pediculus humanus L. (Psocodea: Pediculidae) can be characterized into three deeply divergent lineages (clades) based on mitochondrial DNA. Clade A consists of both head lice and clothing lice and is distributed worldwide. Clade B consists of head lice only and is mainly found in North and Central America, and in western Europe and Australia. Clade C, which consists only of head lice, is found in Ethiopia, Nepal and Senegal. Twenty‐six head lice collected from pupils at different elementary schools in two localities in Algiers (Algeria) were analysed using molecular methods for genotyping lice (cytochrome b and the multi‐spacer typing (MST) method. For the first time, we found clade B head lice in Africa living in sympatry with clade A head lice. The phylogenetic analysis of the concatenated sequences of these populations of head lice showed that clade A and clade B head lice had recombined, suggesting that interbreeding occurs when lice live in sympatry.     

Experimental evidence for costs due to chewing lice in the European bee-eater (Merops apiaster)

Animals frequently host organisms on their surface which can be beneficial, have no effect or a negative effect on their host. Ectoparasites, by definition, are those which incur costs to their host, but these costs may vary. Examples of avian ectoparasites are chewing lice which feed exclusively on dead feather or skin material; therefore, costs to their bird hosts are generally considered small. Theoretically, many possible proximate effects exist, like loss of tissue or food, infected bites, transmission of microparasitic diseases or reduced body insulation due to loss of feathers, which may ultimately also have fitness consequences. Here, we experimentally examined a possible negative impact of 2 feather-eating louse species (Meropoecus meropis and Brueelia apiastri) on male and female European bee-eaters (Merops apiaster) by removing or increasing louse loads and comparing their impact to a control group (lice removed and immediately returned) after 1 month. A negative effect of chewing lice was found on body mass and sedimentation rate and to a lesser extent on haematocrit levels. Males and females lost more weight when bearing heavy louse loads, and were more susceptible to infestations as indicated by the higher sedimentation rate. Our results further suggest differences in sex-specific susceptibility.     

Cattle lice (Anoplura, Mallophaga) in New York: seasonal population changes, effects of housing type on infestations of calves, and sampling efficiency

A year-long survey was made of commercial dairy herds in New York for cattle lice (Anoplura and Mallophaga). All herds were infested with lice. The cattle bitting louse, Bovicola bovis (L.), accounted for about 90% of the observed infestations; infestations of mature animals were most common during the winter months, especially March (26% infested); and infestation rates of calves were high (30-45%) from January through June. Cows that were housed in stanchion barns were about twice as likely to be infested (24.7%) as were those in free stalls (11.1%). Calves housed in individual outdoor hutches had substantially lower infestation rates (4.5%) than calves maintained inside barns in collective stalls and pens (46.0%).     

Transmission dynamics of parasitic sea lice from farm to wild salmon

Marine salmon farming has been correlated with parasitic sea lice infestations and concurrent declines of wild salmonids. Here, we report a quantitative analysis of how a single salmon farm altered the natural transmission dynamics of sea lice to juvenile Pacific salmon. We studied infections of sea lice (Lepeophtheirus salmonis and Caligus clemensi) on juvenile pink salmon (Oncorhynchus gorbuscha) and chum salmon (Oncorhynchus keta) as they passed an isolated salmon farm during their seaward migration down two long and narrow corridors. Our calculations suggest the infection pressure imposed by the farm was four orders of magnitude greater than ambient levels, resulting in a maximum infection pressure near the farm that was 73 times greater than ambient levels and exceeded ambient levels for 30 km along the two wild salmon migration corridors. The farm-produced cohort of lice parasitizing the wild juvenile hosts reached reproductive maturity and produced a second generation of lice that re-infected the juvenile salmon. This raises the infection pressure from the farm by an additional order of magnitude, with a composite infection pressure that exceeds ambient levels for 75 km of the two migration routes. Amplified sea lice infestations due to salmon farms are a potential limiting factor to wild salmonid conservation.     

The potential of carbaryl as a treatment for sea lice infestations of farmed Atlantic salmon, Salmo salar L.

The treatment of sea lice, Lepeophtheirus salmonis infestations on farmed Atlantic salmon, Salmo salar requires regular bathing of the fish in diachlorvos (DDVP), 2,2-dichlorovinyl dimethyl phosphate, with subsequent release to the marine environment of spent pesticide. The toxicity of a possible alternative compound, carbaryl, l-naphthyl N-methylcarbamate) to kill sea lice and Atlantic salmon was examined. Preliminary studies with carbaryl indicate the potential advantage of a reduced treatment dose was outweighed by the greater persistence of both the parent compound and of its toxic degradation product. Hence this carbamate insecticide is unlikely to be considered by regulatory authorities as an alternative treatment for sea lice infestations.     

How sea lice from salmon farms may cause wild salmonid declines in Europe and North America and be a threat to fishes elsewhere

Fishes farmed in sea pens may become infested by parasites from wild fishes and in turn become point sources for parasites. Sea lice, copepods of the family Caligidae, are the best-studied example of this risk. Sea lice are the most significant parasitic pathogen in salmon farming in Europe and the Americas, are estimated to cost the world industry €300 million a year and may also be pathogenic to wild fishes under natural conditions.Epizootics, characteristically dominated by juvenile (copepodite and chalimus) stages, have repeatedly occurred on juvenile wild salmonids in areas where farms have sea lice infestations, but have not been recorded elsewhere. This paper synthesizes the literature, including modelling studies, to provide an understanding of how one species, the salmon louse, Lepeophtheirus salmonis, can infest wild salmonids from farm sources. Three-dimensional hydrographic models predicted the distribution of the planktonic salmon lice larvae best when they accounted for wind-driven surface currents and larval behaviour. Caligus species can also cause problems on farms and transfer from farms to wild fishes, and this genus is cosmopolitan. Sea lice thus threaten finfish farming worldwide, but with the possible exception of L. salmonis, their host relationships and transmission adaptations are unknown. The increasing evidence that lice from farms can be a significant cause of mortality on nearby wild fish populations provides an additional challenge to controlling lice on the farms and also raises conservation, economic and political issues about how to balance aquaculture and fisheries resource management.     

The geographical segregation of human lice preceded that of Pediculus humanus capitis and Pediculus humanus humanus

In order to investigate human-louse phylogeny, we partially sequenced two nuclear (18S rRNA and EF-1 alpha) and one mitochondrial (COI) genes from 155 Pediculus from different geographical origins. The phylogenetic analysis of 18S rRNA and EF-1 alpha sequences showed that human lice were classified into lice from Sub-Saharan Africa and lice from other areas. In both clusters, head and body lice were clearly grouped into two separate clusters. Our results indicate that the earliest divergence within human pediculidae occurred between African lice and other lice, and the divergence between head and body lice was not the result from a single event.     

Severe head lice infestation in an Andean mummy of Arica, Chile

Pediculus humanus capitis is an ancient human parasite, probably inherited from pre-hominid times. Infestation appears as a recurrent health problem throughout history, including in pre-Columbian populations. Here, we describe and discuss the occurrence of pre-Columbian pediculosis in the Andean region of the Atacama Desert. Using a light microscope and scanning electron microscopy, we studied a highly infested Maitas Chiribaya mummy from Arica in northern Chile dating to 670-990 calibrated years A.D. The scalp and hair of the mummy were almost completely covered by nits and adult head lice. Low- and high-vacuum scanning electron microscopy revealed a well-preserved morphology of the eggs. In addition, the excellent preservation of the nearly 1,000-yr-old adult head lice allowed us to observe and characterize the head, antennae, thorax, abdomen, and legs. Leg segmentation, abdominal spiracles, and sexual dimorphism also were clearly observed. The preservation of the ectoparasites allowed us to examine the micromorphology using scanning electron microscopy; the opercula, aeropyles, and spiracles were clearly visible. This case study provides strong evidence that head lice were a common nuisance for Andean farmers and herders. Head lice are transmitted by direct head-to-head contact; thus, this ancient farmer and herder was potentially infesting other people. The present study contributes to the body of research focusing on lice in ancient populations.     

Changes in physiological parameters and feeding behaviour of Atlantic salmon Salmo salar infected with sea lice Lepeophtheirus salmonis

Atlantic salmon Salmo salar L. artificially infected with salmon lice Lepeophtheirus salmonis (Kr?yer 1837) recovered from detrimental physiological changes and skin damage induced by preadult lice as the parasites matured. Growth rates of Atlantic salmon remained unaffected by lice infection, but food consumption decreased with increasing feeding and movement of the lice prior to and post-mating, correlating with the appearance of head erosions and detrimental changes in physiological integrity. Food consumption of the fish increased as the lice moulted to the adult stage and gravid female lice settled in a posterior location on the fish, subsequently reducing the impact of infection and allowing recovery of the skin damage. However, the impact of preadults was limited, as the decrease in food consumption of fish at 21 d post-infection had no effect on either the specific growth rate or condition factor of the fish. Furthermore, the intensity of lice infections at each of the sample days was not correlated with food consumption, specific growth rate or any of the haematological or physiological parameters measured, either before or after infection, indicating that lice intensity was independent of social dominance/subordinance. This work has provided the first evidence that infected fish can recover from the detrimental changes caused by lice infection, even when they are still infected with lice. If fish can survive the preadult stage of lice, then the mortal impact of lice infections is greatly reduced.